WO2020127214A1

WO2020127214A1 - Process for producing a porous fibre composite material, fibre composite material and use of said fibre composite material

Info

Publication number: WO2020127214A1
Application number: PCT/EP2019/085580
Authority: WO
Inventors: Christian Zuber; Thomas Rothermel; Henning Elsäßer; Thomas Reimer
Original assignee: Deutsches Zentrum für Luft- und Raumfahrt e.V.
Priority date: 2018-12-19
Filing date: 2019-12-17
Publication date: 2020-06-25
Also published as: EP3898785B1; DE102018132798A1; EP3898785A1

Abstract

The invention proposes a process for the production of a porous fibre composite material (100), which process comprises: preparing a fibre structure (102) that has been or is infiltrated with a liquid mixture comprising a polymer resin (108), an organic solvent (112), in particular isopropanol (114), and a formaldehyde former (116); curing (122) the liquid mixture (104) to form a fibre-polymer resin material having a pore structure (124); infiltrating (106) the fibre-polymer resin material having a pore structure (124) with water (134); and annealing (138) the fibre-polymer resin material having a pore structure (124) which is infiltrated with water (134).

Description

Process for producing a porous fiber composite material, fiber composite material and use of a fiber composite material

The present invention relates to a method for producing a porous fiber composite material.

The invention further relates to a fiber composite material produced by a method according to the invention.

The invention further relates to the use of a fiber composite material according to the invention as a thermal protection material.

A composite material is known from DE 3613990 A1, which is produced by pressing multilayer thermosetting prepregs from reinforcing materials impregnated with thermosetting resin systems. One or more epoxy resin prepregs are pressed with one or more novolak prepregs.

DE 1 669 845 A discloses a process for producing preformed molding compositions from curable synthetic resins which are soluble in water and / or organic solvents, and also pulling and / or reinforcing materials and other customary additives such as lubricants and dyes. The resin is mixed either in the form of a solution in a solvent or in powder form with the addition of a solvent with the usual additives, optionally also with formaldehyde-releasing compounds such as hexamethylenetetramine and with the fillers and / or reinforcing materials without substantial heat, after which so much Water is worked in until the mixture has become malleable. After that, the mixture is passed through a suitable one

Device preformed and then brought to the desired degree of flow by drying. US Pat. No. 5,658,360 A discloses a method for producing uncured cast abrasive articles which have a small proportion of volatile organic chemicals. Water is used as a temporary binder during production.

US 2013/0059974 A1 discloses a phenolic resin substance which comprises a phenolic resin of the novolak type, a phenolic resin of the resol type, hexamethyl-tetramine, graphite and fiber-containing filling materials.

The invention has for its object to provide a method with which a fiber composite material can be produced, in which the fiber spaces are filled with a low density material and which can be carried out with a simple structure.

This object is achieved by a method for producing a porous fiber composite material, the method comprising:

Providing a fiber structure which is or will be infiltrated with a liquid mixture comprising a polymer resin, an organic solvent, in particular isopropanol, and a formaldehyde former;

Curing the liquid mixture to form a fiber-polymer resin material with a pore structure;

Infiltrating the pore-structure fiber polymer resin material with water; and

Annealing the water-infiltrated fiber polymer resin material with a pore structure.

The pore-structure polymer resin material preferably has one

spongy network structure.

During the hardening of the liquid mixture with formation of the fiber-polymer resin material with a pore structure, the porous fiber composite material is preferably partially formed. During the annealing of the water infil- trier fiber-polymer resin material with a pore structure, the formation (reaction) of the porous fiber composite material is particularly ended.

"Porous" in the sense of the invention means that the material characterized thereby (namely fiber-polymer resin material with pore structure and the fiber composite material) has a ratio of void volume to total volume of 20% or more, in particular 40% or more. The total volume is preferably indicated by the sum of the void volume and the clean volume of the solid. The fibers in the fiber-polymer resin material with a pore structure and the porous fiber composite material are in particular non-porous.

A porosity can be determined according to a preferred characterization method by mercury porosimetry. Here, a non-wettable liquid, for example mercury, penetrates into the pores of a material to be characterized under high pressure. A pore size of the pores of the

characterizing material is determined as a function of an external pressure by means of a porosimeter. The porosimeter is a device used to measure the air permeability of the material to be characterized.

According to a preferred embodiment, the porosity of the porous fiber composite material resulting from the process according to the invention is in a range from approx. 50% to approx. 60%, particularly preferably in a range from approx. 54% to approx. 57%.

The porous fiber composite material is preferably open-pored, with cavities of the material being connected to an environment.

The porous fiber composite material is preferably both mesoporous with pore sizes from 2 nm to 50 nm and macroporous with pore sizes greater than 50 nm. The cavities in the porous fiber composite material are preferably randomly distributed and / or homogeneously distributed.

“Liquid mixture” is to be understood as a chemical mixture of at least the polymer resin, the organic solvent and the formaldehyde generator. At least so much organic solvent is contained that the liquid mixture is flowable.

In particular, the liquid mixture is homogeneous and is present as a solution of the polymer resin and the formaldehyde former in the organic solvent. However, depending on the polymer resin and quantitative proportions, it can also be provided that the liquid mixture is a dispersion, at least some of the polymer resin and / or the formaldehyde former floating in the organic solvent in finely divided form.

When the liquid mixture hardens, this becomes the same with the liquid

Mixture of infiltrated fiber structures preferably heated. In particular, there is a chemical crosslinking reaction, for example a polymerization reaction. The fibers of the fiber structure preferably do not take part in the reaction. In particular, a polycondensation reaction takes place.

"Tempering" in the sense of the invention is a heat application of the material to be tempered, wherein optionally an increased pressure can be applied externally to the material to be tempered or a vapor pressure builds up due to an implementation of the tempering in a pressure-tightly closed container. If the temperature rises or heat is applied, room temperature (20 ° C) is the preferred starting temperature.

A pressing, in which fibers can be damaged, is preferably unnecessary. The annealing can preferably be carried out according to one of the following variants:

Positioning the water-infiltrated fiber-polymer resin material with a pore structure in a container, pressure-tightly closing the container and then heating the container and the water-infiltrated fiber-polymer resin material therein, in particular creating a vapor pressure which essentially prevents boiling of the water; or

Positioning the water-infiltrated fiber-polymer resin material with a pore structure in a container, sealing the container - in particular with a fluid-tight membrane - positioning the sealed container in an autoclave and applying a pressure, the application of the pressure in particular essentially boiling the water is prevented.

It can also be provided that the water-infiltrated fiber-polymer material with pore structure in the pressure-tightly closed container (according to the first-mentioned variant) is externally pressurized by an autoclave.

In particular, the water does not prevent the crosslinking reaction, but rather ensures a controlled course of the process due to its heat capacity.

The fluid-tight membrane prevents a volume reduction of the water-infiltrated fiber polymer resin material with a pore structure due to vaporization.

The organic solvent preferably does not participate in chemical reactions during curing. However, the organic solvent influences the chemical reaction in that it completely crosslinks the polymer resin during the curing of the liquid

Prevents mixture. The formaldehyde generator reacts to formaldehyde under suitable reaction conditions, preferably heating.

By using organic solvent in the liquid

Mixture reduces the amount of reacting substances and during curing a material with reduced density is created compared to a curing process with little or no solvent. As a result, a fiber-polymer resin material with a pore structure can be formed during curing, which also has a reduced density compared to a solid material.

In the sense of the invention, the porous fiber composite material is a fiber material, a mesh-like structure comprising coherent particles of different sizes made of chemically crosslinked polymer resin being present in the spaces formed between the fibers. The particles preferably have an irregular shape at the micrometer level.

Because the fiber-polymer resin material with a pore structure is infiltrated with water before the tempering, the energy released during the tempering, in particular crosslinking energy, is absorbed by the water in the form of heat. The high thermal capacity of the water is used in particular. In addition, water does not hinder a chemical crosslinking reaction of the polymer resin, which occurs during the annealing, compared to other solvents. Crosslinking energy can arise in exothermic crosslinking reactions.

The fiber structure can be provided in the form of a felt, in particular a carbon felt, in the form of ceramic felt layers, or as a fleece. In particular, a textile fiber structure, for example in the form of a braid, a knitted fabric or a fabric, is provided. The fibers of the fiber structure are preferably carbon fibers. Alternatively, one of the following fibers or mixtures thereof or

Mixtures of these are used with carbon fibers: polymer fibers, glass fibers, ceramic fibers, natural fibers.

The fibers can be used as long fibers or short fibers. Preferred polymer fibers are phenolic resin fibers.

For example, a fiber structure is provided in the form of one or more layers, which are produced, for example, by a wet nonwoven process.

It may be favorable if the fiber structure comprises, comprises or is formed from a mixture of short fibers and comminuted fibers, for example into one or more wet nonwovens.

The comminuted fibers are preferably ground fibers.

The short fibers preferably have an average length of approximately 6 mm to approximately 10 mm.

An average length of the comminuted fibers is preferably in a range from approximately 0.25 mm to approximately 0.35 mm, for example approximately 0.3 mm.

It can be advantageous if the fiber structure comprises or is formed from phenolic resin fibers and a binder.

A preferred binder is polyvinyl alcohol fibers. The phenolic resin fibers are preferably cross-linked phenol-aldehyde fibers, which are produced in particular by acid-catalyzed cross-linking of melt-spun novolak resin.

The phenolic resin fibers preferably have a fully cross-linked three-dimensional amorphous structure.

It can be advantageous if the phenolic resin fibers consist of approx. 76% by weight

Carbon, about 18 wt .-% oxygen and about 6 wt .-% hydrogen.

Phenolic resin fibers, which are available under the product name "Kynol® Novoloid fibers" from the company Kynol Europa GmbH, have proven to be particularly favorable.

A porous fiber composite material, the fibers of which are carbon fibers, is preferably temperature stable up to 300 ° C.

In embodiments in which the fiber structure comprises or is formed from phenolic resin fibers, the resulting fiber composite material preferably has a thermal conductivity reduced by a factor of 5 or more, in particular by a factor of 6 or more, compared to a fiber composite material in which instead of the phenolic resin fibers

Carbon fibers were used.

The direction of thickness is preferably defined perpendicular to an outer surface of the fiber composite material.

For example, the thermal conductivity of the fiber composite material with phenolic resin fibers in the thickness direction is 0.0423 W / (m-K).

A thermal conductivity of the fiber composite material with carbon fibers in the thickness direction is preferably 0.256 W / (mK). When exposed to heat, for example from temperatures such as those prevailing when the earth re-enters, the phenolic resin fibers preferably pyrolyze to carbon fibers and / or are converted to carbon fibers. The thermal protection effect can be optimized in this way, in particular since energy is converted as soon as the phenolic resin fibers are converted to carbon fibers.

The pyrolysis of the phenolic resin fibers preferably takes place at temperatures from approximately 400 ° C. to approximately 3000 ° C.

The conversion of the phenolic resin fibers to carbon fibers is preferably an endothermic decomposition.

The carbon fibers resulting from the reaction of the phenolic resin fibers are, for example, porous carbon fibers.

The resulting fiber composite material is in particular comparable to a fiber composite material which was produced using a fiber structure made of carbon fibers.

A char layer which, for example, with a heat flow density of approx.

3 MW / m ² in a plasma wind tunnel on a surface of the

Fiber composite material is preferably comparatively thin.

A ratio of a total thickness of the fiber composite material (virgin material) and a thickness of the char layer is preferably 4: 1 or more, in particular 4.5: 1 or more.

In particular, the ratio of the thickness of the fiber composite material overall (virgin material) and the thickness of the char layer is 5: 1 or less, in particular 4.6: 1 or less. The porous fiber composite material in the non-pyrolyzed state up to 300 ° C. and / or in the pyrolyzed state can be processed in particular by means of mechanical methods. Mechanical methods include sawing, cutting, turning and / or drilling.

A fiber structure, as is conventionally used for the production of fiber composite materials, is preferably used.

In particular, materials in the form of a fiber structure can also be used, which are conventionally used as insulation material for high-temperature furnaces or in other high-temperature applications. Fiber structures comprising short fibers can also be used with preference.

According to a preferred embodiment of the method, a fiber structure is provided and this is infiltrated with the liquid mixture comprising a polymer resin, an organic solvent and a formaldehyde former.

Alternatively, pre-impregnated fiber structures, so-called "prepregs", can also be used. These pre-impregnated fiber structures are already impregnated with a polymer resin. When using pre-impregnated fibers, it may be sufficient if an organic solvent and the formaldehyde former are added to these pre-impregnated fibers. In particular, the polymer resin is then at least partially dissolved in the organic solvent, for example in isopropanol.

A density of the porous fiber composite material is preferably in a range from approximately 0.35 g / cm ³ to approximately 0.45 g / cm ³ , in particular approximately 0.4 g / cm ³ . The porous fiber composite material preferably has an airgel-like structure in the intermediate spaces between the fibers. By infiltrating the fiber-polymer resin material with a pore structure with water prior to tempering, a substantial temperature rise within the porous fiber composite material which arises, which could result in material damage in the porous fiber composite material, can be avoided during the tempering.

The porous fiber composite material is preferably suitable as a flame-retardant structure, for example as a thermal protection material for re-entry of missiles into the earth's atmosphere. For this purpose, blocks made of the porous fiber composite material can, for example, be glued to an area to be protected.

It is important here that the polymer resin and the resulting chemically crosslinked material have a low thermal conductivity.

Because of the pore structure, which is retained in particular from its formation in the fiber-polymer resin material with a pore structure, of the fiber composite material with a low density, even at high temperatures, such as, for example, from over 3000 ° C., for example from over 10,000 ° C., upon reentry into the earth's atmosphere, first the surface of a component made of the porous fiber composite material is heated, before further areas inside are heated. Pyrolysis takes place. The porous fiber composite material in the pyrolyzed state or pyrolysis state can then melt, sublimate or oxidize.

Carbon atoms of the porous fiber composite material in pyrolyzed

Conditions can be emitted into an interface between an ablator surface and a shock front and reduce a radiative energy input into the thermal protection material at the interface.

Alternatively, the porous fiber composite material can also be used as other fire protection material. Due to its low thermal conductivity, it is also generally suitable as an insulation material.

When the liquid mixture cures to form a fiber-polymer resin material with a pore structure, the polymer resin is preferably initially incompletely crosslinked. The fiber-polymer resin material with a pore structure has - in particular - despite an incomplete chemical crosslinking reaction - sufficient mechanical strength so that it can be handled in the further process.

The chemical crosslinking reaction is preferably a polymerization reaction, in particular a polycondensation.

The fiber composite material can also be used as a core material for a sandwich structure for certain applications. The sandwich structure preferably comprises a first layer element, a second layer element and an intermediate core element made of the core material.

The formaldehyde generator preferably comprises urotropin or is urotropin. Urotropin - also known as hexamethylenetetramine - as a formaldehyde generator is less dangerous for human and / or animal organisms than most other available alternative formaldehyde generators and / or formaldehyde and is therefore easier to handle.

The curing is preferably carried out by heating the liquid mixture in a pressure-tightly closed die and / or heating the liquid mixture with external pressure being applied to the liquid mixture, in particular in an autoclave.

In embodiments in which the curing is carried out in a pressure-tight closed die, the liquid mixture in the pressure-tight closed die is preferably heated in an oven. During the hardening of the liquid mixture to form the fiber-polymer resin material with a pore structure, the resulting steam remains in the die. This builds up a vapor pressure. The vapor pressure prevents boiling and / or excessive evaporation of the polymer resin, the organic solvent and in particular the formaldehyde generator.

To prevent the pressure-tight closed die from bursting due to an internal pressure that arises, walls of the pressure-tight closed die are preferably solid.

As an alternative to heating the pressure-tight closed die without further external pressurization, it can be provided that the liquid

Mixture in the pressure-tight closed die in an autoclave is externally pressurized.

In embodiments in which curing is carried out in an autoclave, a container is closed, in particular with a fluid-tight and / or flexible membrane, and pressure is applied to the liquid mixture in the autoclave. The pressurization preferably prevents the polymer resin and the organic solvent - and in particular the formaldehyde former - from boiling. Evaporation of the organic solvent or other components of the liquid mixture is in particular additionally prevented by the fluid-tight and / or flexible membrane.

The method offers the advantage that a size or shape of the porous fiber composite material is only given by the size of the die or autoclave and the size and shape is otherwise freely scalable or selectable.

The curing is preferably carried out at a temperature of approximately 120 ° C. to approximately 160 ° C., in particular at a temperature of approximately 140 ° C. to approximately 150 ° C., for example at a temperature of approximately 145 ° C. As a reac tion times have proven to be particularly suitable for curing from 4 hours or more, the reaction times - depending on the size and shape of the fiber structure - may vary. At the temperatures mentioned, chemical crosslinking preferably takes place at least partially in a controlled manner.

This creates a three-dimensional network, but the networking is not yet complete.

By using the organic solvent, however, curing can also be carried out at a temperature of approximately 225 ° C. without complete crosslinking taking place.

Despite the organic solvent, there is a curing reaction

Polymer resin instead.

The 4 h mentioned have proven, for example, for a fiber structure with dimensions of 170 mm x 170 mm x 50 mm to be a particularly suitable curing time for the liquid mixture.

When curing in an autoclave, the curing is preferably carried out under a pressure of approximately 10 bar to approximately 20 bar, preferably approximately 15 bar. The increased pressure ensures that no organic solvent can escape. The increased pressure also has the advantage that a rate constant of the chemical crosslinking reaction is greater than at room pressure. The crosslinking is therefore faster, in particular by a factor of approximately 4 or more, than with curing under room pressure.

The curing is preferably carried out in a closed, pressure-resistant die. External mechanical pressure is preferably applied. In particular, the vapor pressure of the organic solvent results in faster crosslinking. A membrane is preferably formed which minimizes or prevents the organic solvent from escaping.

Pressure, for example in an autoclave, prevents the organic solvent from boiling.

A proportion of formaldehyde generator is preferably in a range from approximately 0.4% by weight to approximately 10.0% by weight, preferably approximately 0.5% by weight to approximately 1.5% by weight. , in particular from approximately 0.8% by weight to approximately 1.2% by weight, based on a mass of the polymer resin used.

It can be advantageous if the polymer resin and the organic solvent are present in the liquid mixture, in particular before the addition of the formaldehyde former, in a ratio of the mass of the polymer resin to the mass of the organic solvent of approximately 2 to 3 to approximately 3 to 2 .

For example, the polymer resin and the organic solvent are mixed in a mass ratio of about 1 to 1.

With such ratios of polymer resin and organic solvent, a proportion of the polymer resin is sufficient for a chemical crosslinking reaction to take place during curing. The proportion of solvent is preferably high enough to produce a structure with a lower density compared to cured, undiluted polymer resin. At a high degree of dilution, a crosslinking reaction of the polymer resin occurs in particular due to the formaldehyde former.

The polymer resin is preferably a phenolic resin or an epoxy resin. A phenolic resin has the advantage that during pyrolysis residual carbon is formed and / or it is particularly suitable as a burning material. Preferably, the organic solvent is removed with water before infiltrating the pore-structure fiber polymer resin material. In particular, the organic solvent is removed by heating the fiber polymer resin material having a pore structure, particularly at a temperature ranging from 95% to 105% of the boiling point of the organic solvent.

When using isopropanol, the isopropanol is removed, for example, at about 80 ° C. For this purpose, the fiber-polymer resin material with pore structure, which still contains isopropanol, is preferably stored at about 80 ° C. until a constant mass is set in a tempering furnace.

It can be favorable if the infiltration of the fiber polymer resin material with pore structure with water under vacuum, preferably under the application of a negative pressure of approx. 2 mbar to approx. 200 mbar, in particular in particular from approx. 2 mbar to approx. 10 mbar, for example approx 5 mbar, to a container containing the fiber-polymer resin material with a pore structure.

A reaction to form a porous network preferably takes place completely or until the reaction is terminated, wherein structures of the porous network have an average diameter of approximately 500 nm or less, preferably approximately 300 nm or less, in particular approximately 150 nm or less. The reaction to form the porous network, particularly a polymerization reaction, begins during the curing of the liquid mixture.

Structures of the porous network preferably form at approximately 145 ° C.

The mean diameter is preferably given as an arithmetic mean. However, it can also be provided that the mean diameter is related to the median of the diameter distribution. The diameter refers in particular to the shortest connection between two surfaces. After the tempering, the water is preferably evaporated by heating in a range from approximately 80 ° C. to approximately 100 ° C., preferably approximately 90 ° C. For this purpose, the material is stored, for example, at approximately 5 mbar in a desiccator or in another container that is subjected to a vacuum. Alternatively, the water can be steamed off in an oven, for example, even at normal pressure.

The features and / or advantages mentioned in connection with the method according to the invention apply equally to the fiber composite material according to the invention.

It can be advantageous if the fiber composite material comprises phenolic resin fibers, which can be converted and / or converted into carbon fibers, in particular when exposed to heat while maintaining a fiber structure.

For example, the phenolic resin fibers pyrolyze at temperatures in a range from about 400 ° C to about 3000 ° C (exposure to heat).

The effect of heat is preferably understood to mean that the fiber composite material is exposed to temperatures of 400 ° C. or more, in particular approximately 900 ° C. or more, for example approximately 1500 ° C. or more, for example under an inert gas atmosphere.

An inert gas atmosphere is used to simulate conditions that exist when the earth re-enters the atmosphere.

The fiber composite material is particularly exposed to high temperatures as thermal protection material when it re-enters the earth's atmosphere. The invention further relates to the use of a fiber composite material according to the invention as a thermal protection material.

The features and / or advantages mentioned in connection with the method according to the invention apply equally to the use according to the invention.

Further preferred features and / or advantages of the invention are against the following description of the drawing of exemplary embodiments.

Show it :

Fig. 1 is a flowchart of a method for producing a porous

Fiber composite material;

Fig. 2 is a schematic illustration of a die for curing a fiber structure infiltrated with a liquid mixture for use in the method described in Fig. 1;

Figure 3 is a schematic representation of an autoclave for curing a fiber structure infiltrated with a liquid mixture for use in the method described in Figure 1;

FIG. 4 shows an electron micrograph of a porous fiber composite material produced using the method from FIG. 1;

FIG. 5 shows a further electron micrograph of a porous fiber composite material, produced using the method from FIG. 1; and

6 shows a further electron micrograph of a porous fiber composite material, produced using the method from FIG. 1. A flow diagram of a method for producing a porous fiber composite material 100 is shown schematically in FIG. 1.

First, a fiber structure 102 is provided. In the present case, a carbon fiber structure 103 comprising carbon fibers, which form a felt or a nonwoven or some other textile fabric, is used for this purpose. Alternatively, other forms of a textile fiber structure 102 can also be used. For example, the fiber structure 102 is a braid, a woven fabric, a knitted fabric or a woven fabric.

Alternatively, a fiber structure 102 made of glass fibers, polymer fibers, ceramic fibers, natural fibers or mixtures thereof or mixtures of one or more of the fibers mentioned with carbon fibers can also be provided.

Preferred polymer fibers are phenolic resin fibers.

The phenolic resin fibers are preferably based on novolak (based on phenolic resin), which is melt-spun and then catalyzed by an acid

Crosslinking is cured.

A preferred chemical composition of the phenolic resin fibers is: approx.

76 wt .-% carbon, about 18 wt .-% oxygen and about 6 wt .-% hydrogen.

Phenolic resin fibers with the product name "Kynol® Novoloid fibers" from the company Kynol Europa GmbH have proven to be particularly suitable.

The fiber structure 102 is preferably produced by means of a wet fleece process. For example, wet nonwovens are produced from a mixture of short phenolic resin fibers, in particular with an average length in a range of about 6 mm and about 10 mm, and ground phenolic resin fibers with an average length of about 0.3 mm and polyvinyl alcohol fibers as binders.

The binder melts during a drying process to produce the fiber structure 102.

The fiber structure 102 is infiltrated with a liquid mixture 104 (infiltrating 106).

The mixture 104 comprises a polymer resin 108 in the form of a phenolic resin 110, an organic solvent 112 in the form of isopropanol 114 and a formaldehyde former 116 in the form of urotropin 118.

The organic solvent 112 serves to dilute the polymer resin 108.

Isopropanol 114 has the advantage that the phenolic resin 110 and urotropin 118 are readily soluble in it and, due to its comparatively low boiling point of 82.6 ° C and high vapor pressure of 42.6 hPa, it is easy to evaporate at 20 ° C. Evaporation will be carried out in more detail later.

The liquid mixture 104 is prepared before infiltrating 106.

For this purpose, phenolic resin 110 and isopropanol 114 are mixed in a mass ratio of 1: 1. About 1% by weight of urotropin 118 are added to this mixture, based on a mass of the phenolic resin 110 used. The urotropin 118 is ground before the addition, whereby a faster dissolution of the urotropin 118 in the isopropanol 114 can be achieved. For infiltration 106, the fiber structure 102 is placed in a container 120 (cf.

2 and 3) infiltrated with the mixture 104 at a reduced pressure of approximately 200 mbar. In the case of a fiber structure 102 with dimensions of 300 mm × 300 mm × 50 mm, an infiltration time is, for example, approximately 2 hours. After infiltrating 106, the container 120 is closed.

Following infiltration 106, the liquid mixture 104 is cured to form a fiber-polymer resin material having a pore structure 124 (curing 122). Hardening 122 is carried out in an autoclave 126 (see FIG. 3) or in a pressure-tightly closed die 128 (FIG. 2). However, it can also be provided that the liquid mixture 102 in the pressure-tightly closed die 128 is externally pressurized in an autoclave 126.

The times specified in connection with the method can vary depending on the size and shape of the fiber structure 102.

When hardening 122 in the pressure-tightly closed die 128 (cf. FIG. 2), the die 128 is heated in a tempering furnace for approximately 16 hours or more at approximately 145 ° C. After the die 128 has cooled completely, the fiber-polymer resin material 124 formed therein is removed from the mold.

Due to the pressure-resistant and, in particular, also fluid-tight design of the pressure-tight closed die 128, the resulting steam cannot escape from the pressure-tight closed die 128 and a vapor pressure builds up. The vapor pressure minimizes boiling of the polymer resin 110 and the organic solvent 112. A volume of the organic solvent 112 is kept substantially constant.

In the present case, the pressure-tightly closed die 128 is of solid design in order to be able to withstand an internal pressure arising during the hardening 122 of the liquid mixture 104 in the pressure-tightly closed die 128 without bursting. When hardening 122 in an autoclave 126 (cf. FIG. 3), a sealed container 120 is introduced into an autoclave 126, a membrane 130 being used here in the present case for the fluid-tight sealing of the fiber structure 102 infiltrated with the liquid mixture 104. This prevents the organic solvent 112 from evaporating during the curing 122 of the liquid mixture 104.

In an autoclave process, a pressure of approx. 15 bar is built up in the autoclave 126 and then, in particular at a maximum heating rate (within approx. 30 min), heated to a temperature of approx. 145 ° C. The set temperature and the set pressure are kept constant for a curing time, for example for about 4 hours or more.

The autoclave 126 is then cooled to approx. 25 ° C. The pressure in the autoclave 126 is kept at approx. 15 bar until it is completely cooled to room temperature (approx. 20 ° C). After cooling to room temperature, the pressure of approx. 15 bar is released and the resulting fiber-polymer resin material with pore structure 124 is removed from the mold.

After the formation of the fiber polymer resin material with pore structure 124 during curing 122, the isopropanol 114 is removed (removal 132).

For this purpose, the fiber polymer resin material containing pore structure 124, which after curing 122 still contains isopropanol 114, is stored in an annealing oven at approx. 80 ° C. until a constant mass has been established and / or the isopropanol 114 has been completely evaporated .

The fiber polymer resin material with pore structure 124 is then infiltrated with water 134 (infiltrate 136). For this purpose, the fiber polymer resin material with pore structure 124 is stored in a container, in the present case a desiccator 135, for, for example, approximately 60 minutes or more at approximately 5 mbar. The desiccator 135 is flooded with water to infiltrate (136). The fiber-polymer resin material with pore structure 124 is stored for approx. 100 min or more under water 134 at a pressure of approx. 5 mbar in the desiccator 135. After the vacuum has been released, the fiber polymer resin material with pore structure 124 is stored, for example, for a further 150 minutes or more under water 134 before the fiber polymer resin material with pore structure 124 is removed from the desiccator 135 and placed in a water-filled container.

The water-filled container is closed for a tempering step (tempering 138) and positioned in an autoclave 126.

In a further autoclave process, a pressure of approx. 15 bar is built up and the autoclave 126 is heated to approx. 160 ° C. after the pressure has been reached, in particular at the maximum heating rate. The set temperature and the set pressure will, for example, last for about 6 hours or more. The autoclave 126 is then cooled to about 25 ° C. (for example in about 20 minutes). The pressure is kept at about 15 bar until it has completely cooled to room temperature.

The tempering 138 can alternatively also be carried out in a pressure-resistant die 128 which is filled with water in an oven without external pressure.

After tempering 138, water 134 is removed (evaporation 140).

For this purpose, the fiber composite material 100 is dried at about 90 ° C. in an annealing oven. The evaporation 140 is carried out until the porous fiber composite material 100 has a constant mass.

The fiber composite material is suitable for use as a thermal protection material. Ratios of phenolic resin 110, isopropanol 114 and urotropin 118 are given below by way of example. The proportions listed above are given in the table as example 1. The proportions of Examples 1 to 5 are suitable in connection with the process described above.

The various proportions in the table above are each in% by weight. The proportion of phenolic resin 110 and the proportion of isopropanol 114 each relate to a total mass of phenolic resin 110 and isopropanol 114. The proportion of urotropin 118 relates to the mass of the phenolic resin 110 used.

A porous fiber composite material 100 produced by the method described in connection with FIG. 1 can be seen in particular in the electron micrographs shown in FIGS. 4 to 6. The recordings were made with a scanning electron microscope using a secondary electron detector.

A magnification of 5,000 was chosen for the electron micrograph in FIG. 4. In the electron micrograph in Fig. 5, the magnification is 10,000 and in the electron microscope in Fig. 6, the magnification is 50,000.

In embodiments in which the fibrous structure 102 comprises or is formed from phenolic resin fibers, the phenolic resin fibers are under Exposure to heat, especially in a range from about 400 ° C to about 3000 ° C, converted to carbon fibers. In particular, a porous fiber composite material 100 is formed, which comprises carbon fibers.

In particular, the phenolic resin fibers are converted into porous carbon fibers.

A fiber structure and / or overall structure of the fiber composite material is retained.

For example, heat occurs when it re-enters the earth's atmosphere.

When heat is applied to a porous fiber ver

bundle material 100, which comprises phenolic resin fibers, formed a comparatively thin char layer on the surface.

For example, a ratio of a total thickness of the fiber composite material 100 (virgin material) and a thickness of the char layer is 4: 1 or more, in particular 4.5: 1 or more.

In particular, the ratio of the thickness of the fiber composite material 100 as a whole (virgin material) and the thickness of the char layer is 5: 1 or less, in particular 4.6: 1 or less.

The porous fiber composite material 100 with phenolic resin fibers preferably has a reduced thermal conductivity in a thickness direction by a factor of 5 or more, in particular by a factor of 6 or more, compared to a fiber composite material 100 with carbon fibers instead of the phenolic resin fibers. This is an optimized one

Thermal protection effect trained. The thickness direction is preferably defined perpendicular to an outer surface of the fiber composite material 100.

For example, a thermal conductivity of the fiber composite material 100 with phenolic resin fibers in the thickness direction is 0.0423 W / (m-K).

A thermal conductivity of the fiber composite material 100 with carbon fibers in the thickness direction is preferably 0.256 W / (m-K).

The conversion of the phenolic resin fibers to carbon fibers when exposed to heat preferably results in an energy conversion which, in particular, can intensify a heat protection effect of the fiber composite material 100 as a whole.

As can be seen in particular in FIG. 4, structures 150 made of the hardened phenolic resin 110 are network-like with gaps between them. Carbon fibers 152 are embedded therein. The cured phenolic resin 110 preferably has a cross-linked sponge-like structure.

As can be seen in particular in FIG. 5, the structures 150 of the porous fiber composite material 100 have a diameter of 0.1 μm or less.

6 shows in particular that the structures 150 are disordered and spaces between them are cave-like structures. There are no ordered channels.

Reference list of fiber composite material

Fiber structures

Carbon fiber structures

mixture

Infiltrate

Polymer resin

Phenolic resin

organic solvent

Isopropanol

Formaldehyde generator

Urotropin

container

Harden

Fiber polymer resin material with pore structure autoclave

Die

membrane

Remove

water

Desiccator

Infiltrate

Annealing

Evaporate

Thermal protection material

Structures

Carbon fibers

Claims

1. A method for producing a porous fiber composite material (100), the method comprising:

Providing a fiber structure (102) which is or will be infiltrated with a liquid mixture comprising a polymer resin (108), an organic solvent (112), in particular isopropanol (114), and a formaldehyde former (116); Curing (122) the liquid mixture (104) to form a fiber polymer resin material with a pore structure (124);

Infiltrating (106) the fiber polymer resin material with pore structure (124) with water (134); and

Annealing (138) the water-infiltrated fiber polymer resin material with pore structure (124).

2. The method according to claim 1, characterized in that the

Formaldehyde generator (116) comprises urotropin (118) or is urotropin.

3. The method according to any one of the preceding claims, characterized in that the curing (122) by heating the liquid mixture (104) in a pressure-tight closed die (128) and / or heating the liquid mixture (104) with external exposure to the liquid mixture (104) with pressure, in particular in an autoclave (126).

4. The method according to any one of the preceding claims, characterized in that the curing (122) at a temperature of approximately 120 ° C to approximately 160 ° C, preferably approximately 140 ° C to approximately 150 ° C, in particular approximately 145 ° C is carried out. 5. The method according to any one of the preceding claims, characterized in that a proportion of formaldehyde generator (116) in a range from about 0.4 wt .-% to about 10.0 wt .-%, preferably in one

Range from approx. 0.5% by weight to approx. 1,

5% by weight, in particular in a range from approximately 0.8% by weight to approximately 1.2% by weight, based on a mass of the polymer resin (108) used.

6. The method according to any one of the preceding claims, characterized in that the polymer resin (108) and the organic solvent (112) in the liquid mixture (104), in particular before adding the formaldehyde former (116), in a ratio of the mass of the poly Mer resin (108) to mass of the organic solvent (112) from about 2 to 3 to about 3 to 2, in particular from about 1 to 1, are present.

7. The method according to any one of the preceding claims, characterized in that the polymer resin (108) is a phenolic resin (110) or an epoxy resin.

8. The method according to any one of the preceding claims, characterized

characterized in that the fiber structure (102) comprises or is formed from phenolic resin fibers.

9. The method according to any one of the preceding claims, characterized in that the organic solvent (112) is removed before infiltrating (106) of the fiber polymer resin material with pore structure (124) with water (134), preferably by heating the fiber polymer resin material with a pore structure (124), in particular at approximately 80 ° C. to approximately 100 ° C., for example at approximately 80 ° C.

10. The method according to any one of the preceding claims, characterized in that during the annealing (138) a reaction to form a porous network takes place completely or until a reaction is terminated, structures (150) of the porous network having an average diameter of approx. 500 nm or less, preferably about 300 nm or less, in particular about 150 nm or less.

11. The method according to any one of the preceding claims, characterized in that after annealing (138) the water (134) by means of He heat in a range from about 80 ° C to about 100 ° C, preferably about 90 ° C. is evaporated.

12. The method according to any one of the preceding claims, characterized in that the curing (122) is carried out under a pressure of about 10 bar to about 20 bar, preferably about 15 bar.

13. The method according to any one of the preceding claims, characterized in that the infiltration (106) of the fiber structure (102) under vacuum, preferably under the application of a negative pressure of approximately 180 mbar to approximately 220 mbar, in particular approximately 200 mbar, to a container (120) containing the fiber structure (102).

14. The method according to any one of the preceding claims, characterized in that the infiltration (106) of the fiber-polymer resin material with pore structure (124) with water (134) under vacuum, preferably under the application of a negative pressure of about 2 mbar to about 200 mbar, in particular from approximately 2 mbar to approximately 10 mbar, for example approximately 5 mbar, is carried out on a container (120) containing the fiber-polymer resin material with a pore structure (124).

15. Fiber composite material (100), produced by a method according to one of claims 1 to 14.

16. Fiber composite material (100) according to claim 15, characterized

characterized in that the fiber material (100) comprises phenolic resin fibers which can be converted and / or converted into carbon fibers (152), in particular when exposed to heat while maintaining a fiber structure.

17. Use of a fiber composite material (100) according to claim 15 or 16 as thermal protection material (144).